Abstract: A rotary sealing device for connecting a fixed gas supply pipe to a tube rotating about its axis. It comprises a first rotary member for receiving the fixed pipe, a second rotary member for receiving and sealing the rotary pipe and fixed to the first member, and a filter placed in a chamber made in the aforementioned members and forming an obstacle to the gas flow and consequently to an overpressure of said gas, opposing the entry into the said chamber of gas coming from outside the device.

Abstract: The invention relates to an apparatus for producing a preform for constituting an optical fiber. This apparatus essentially comprises a glass maker's lathe and a motor which holds and rotates a hollow silica tube, a torch making it possible to heat a cross-section of the tube and which can be translated along the tube and means for supplying the gaseous compounds consisting of silicon chloride, oxygen and doping agents decomposing under the action of the heat. Part of the products obtained is deposited on the walls of the tube. The supply means comprise a pipe entering the tube in axial manner and at the end of which are provided two radially directed arms, which terminate with an outlet normal to the pipe and arm, said pipe moving in translation integrally with the torch.